Tire buffing machines are well known in the tire retreading industry. Conventionally, a tire buffing machine includes both a structure for mounting a used tire and a rasp hub which removes the worn tread from the used tire prior to the retreading process. The used tire is rotated while it is held against the rapidly-rotating rasp hub whose outer perimeter is provided with plural tire rasp blades. When engaged against the used tire, the rasp blades cut or shear small segments of rubber from the worn tread surface area of the tire. In this way, the tire is “buffed” to remove the unwanted used tread and to provide the tire with an evenly-textured surface suitable for retreading.
Tire rasp blades, together with interleaved spacers, are assembled on the periphery of the rasp hub between the hub front and back plates. The back plate is typically provided with plural axially directed support pins for mounting the rasp blades and spacers between the spaced front and back plates. The front plate is then placed on the support pins against the assembled blades and spacers and locked into place. Rasp hubs are typically comprised of five stacked blade sections (wherein each section occupies a 72° circumferential segment) or six stacked blade sections (wherein each section occupies a 60° segment). Thus, each section of the assembled rasp blades is comprised of alternating blades and spacers arranged side-by-side. Furthermore, each section of blades and spacers are angled, or offset, relative to a plane perpendicular to the axis of rotation of the hub to form a cut angle, so that each blade in rotation has an axial cutting swath greater than the width of the blade. The width of a cut swath depends on the cut angle.
During operation, the toothed blades rotating at high speed come into contact and remove the old tread surface of a revolving tire by the rasp blades' cutting and abrading action. But this high speed frictional interaction causes an increase in temperature of the rasp blades. Prolonged exposure to high temperature causes a weakening of the blades and increases the likelihood of blade failure. Blade failure typically involves the breaking off of its teeth or breaking of the blade's body, particularly a portion of the body located adjacent an end of the blade. The likelihood of a substantial increase in the temperature of the rasp hub and, in particular, the blades disposed thereon is increased by the generally closed structure of the rasp hub with the blades and spacers disposed around the hub's outer periphery in a tight fitting arrangement. The present invention operates to reduce the operating temperature of the rasp hub and the blades disposed around its periphery by allowing air to freely circulate through the rasp hub and remove heat from the rasp blades.